The user can set a ConvergenceChecker in BatchLSEstimator
Currently, user can only call setParametersConvergenceThreshold and the ConvergenceChecker will be built from that. We could add a setConvergenceChecker method and would build the default checker only if no checker has been set up by user. We should decide what to do if users call both method. It could be considered an error or they each new call would invalidate settings from previous calls to the other method. This should be documented, though.